Rolling mill control system



Set. 28, 1% R. HULLS ETAL 1 ROLLING MILL CONTROL SYSTEM Filed April 20,1962 3 Sheets-Sheet l FIG. 2.

WITNESSES: INVENTORS Leonard R. Hulls, Derek H. Lennox and George H. a u

' ATTORNEY Se t. 28, 19% L. R. HULLS ETAL 9 3 ROLLING MILL CONTROLSYSTEM Filed April 20, 1962 3 Sheets-Sheet 2 POSITION POSITION GENERATORGENERATOR 11 V SCREWDOWN I6 MOTOR 23 STRAIN k STRAIN m m,

GUAGE GuAGE I OUTPUT UV; THICKNESS I ERROR 22 26 d 2 CIRCUIT A IITRANsDucER AVERAGING M ,6 w, a CIRCUIT 22 GUAGE GuAGE MONITOR MONITOR W3 is AvERAGING CIRCUIT 22b, I 22b 25 M h AGING A ER TRANSDUCER: V z- 2|I CIRCUIT 20 y 220 220 REEL REEL MOTOR MOTOR III TENsIoN 0J LIMITCIRCUIT Fi g. 3

M- R965 L. R. HULLS ETAL 3,208,251

ROLLING MILL CONTROL SYSTEM Filed April 20, 1962 3 Sheets-Sheet 3 UnitedStates Patent 3,208,251 ROLLING MILL CONTROL SYSTEM Leonard R. Hulls,Fort Washington, Pan, and Derek H. Lennox, Hamilton, Untario, and GeorgeH. Samuel, Burlington, Ontario, Canada, assignors to CanadianWestinghouse Qornpany, Limited, Hamilton, Ontario, Canada Filed Apr. 29,1962, Ser. No. 18%091 Claims priority, application Canada, May 3, 1961,822,622 11 Claims. (Cl. 72 11) The present invention is concerned withimprovements in or relating to control systems for rolling mills.

Material entering a rolling mill may vary in thickness, hardness andother properties along its length and it is customary to try tocompensate for these variations of the ingoing material so that theoutgoing material will be of as constant thickness as possible.

Accordingly, various control systems have been proposed in which thethickness of the outgoing material is measured continuously and thespacing of the mill rolls, and/or the tension on the material beingrolled are adjusted so as to maintain the outgoing thickness as constantas possible. In recent years the users of the rolled material haverequired that the material be rolled to within closer and closer limits,owing to the advantages obtained in their own use of the material.

With the increasing speed of mills and this requirement for addedaccuracy of rolling, it has become more and more necessary to provide afast response in the mill control system. In order to obtain such fastresponse, and also to reduce the errors incurred in measurement, anumber of proposals have been made hitherto whereby the outgoingthickness is measured at the nip of the Work rolls. This measurement canbe made directly or indirectly.

An application in the United State Patent Office, S.N. 761,495, now US.Patent No. 3,062,078, by Leonard Hulls filed September 17, 1958discloses a method in which the measurement is made indirectly, thespecification describing a system that makes use of the fact that a millobeys Hookes Law, and that therefore during its operation the spacingbetween the rolls is equal to their spacing when unloaded plus anadditional spacing proportional to the strain of the mill. An electricsignal representing the unloaded position of the rolls is added to asignal representing the correct proportion of the total strain betweenthe rolls, the resulting signal being compared with a reference signaland the difference between the two signals giving an error signalrepresenting the amount by which the actual outgoing thickness of thematerial differs from the desired outgoing thickness. This error signalis used to control the tension of the material passing between the rollsand the spacing at which the rolls are set.

British patent specification No. 743,233 discloses a direct method ofmeasurement, the specification describing apparatus for maintaining theaxial distances between the lower and upper work rolls of the rollingmill at a preset value during the rolling period, the apparatusincluding measuring devices which are disposed between speciallyprovided extensions of the rolls. The measuring devices are responsiveto divergence of the actual distance of these bearing extensions fromthe preset value and causes operation of control means to move the upperroll so as to return the said axial distance to the preset value. In thespecific embodiment described each measuring device consists of an airgauge which actuates a differential pressure relay in known manner.

It is an object of the present invention to provide a rolling millcontrol system of new form.

'ice

It is another object of the present invention to provide a rolling millcontrol system of new form that is inherently more capable of accuraterolling than comparable systems provided hitherto.

According to the present invention there is provided a control systemfor a rolling mill, the mill comprising a pair of work rolls betweenwhich passes the material to be rolled, the system comprising means formaking a measurement that is effectively a direct measurement of thedistance between the axes of rotation of the work rolls and forproducing a first electric signal representative thereof, means forproducing a second signal representative of the separating forceproduced between the rolls with the material passing between them, meansutilizing the said first and second signals in the production of a thirdsignal representative of the output thickness of material that haspassed between the rolls, and means utilizing the said third signal forcontrolling the rolling of the mill.

A specific embodiment of the invention will now be described, by way ofexample, with reference to the accompanying diagrammatic drawings,wherein:

FIGURE 1 is a side elevation of the mill;

FIGURE 2 is an elevation of the mill taken on the line 2-2 of FIGURE 1;

FIGURE 3 is a schematic representation of a control system for the millof FIGURES 1 and 2; and

FIGURE 4 is a longitudinal section showing a specific form of transducerfor use in the control system of FIG- URE 3 and mounted in a roll chockof the mill.

The mill illustrated is a reversing rolling mill comprisa mill frame 1in which are rotatably mounted a pair of working rolls 2 and 3 andrespective co-operating back-up rolls 4 and 5. A strip 6 of materialthat is to be reduced in thickness passes between the Work rolls 2 and 3from a right-hand side unwind reel 7 to a left-hand take-up reel 8. Thework rolls 2 and 3 are mounted for rotation with their necks inrespective work roll chocks 9 and 10, which are mounted for slidingmovement in slots 11 of the frame 1. The upper back-up roll 4 is mountedfor rotation by plummer blocks 12, which also slide vertically in therespective slots 11.

The postions of the blocks 12, and thus the spacing of the rolls 2 and3, are established by screws 13 which pass through correspondingscrew-threaded bores in the frame 1, so that rotation of the respectivepinions 14 mounted on the upper ends of the screws cause them to movevertically through the frame. The pinions 14 are rotated by means ofrespective worm gears 15 mounted on the shafts of their motors 16. Astrain gauge 17 is interposed between the end of each screw 13 and itspoint of contact with the respective plummer block 12, the gaugemeasuring the force of each screw 13 on its block 12 due to theseparating force produced between the rolls 2 and 3 by the strip 6. Anextension shaft 18 is mounted on the upper surface of each pinion 14 anddrives a position generator 19 which produces an electric signalrepresentative of the rotation and displacement of the screws 13relative to the frame 1, and hence representative of the height of thegap between the rolls 2 and 3 when no material is present between them.

For reasons which will be described below a mill in accordance with thisinvention will generally be provided either with the'strain gauges 17 orwith the position generators 19, both being shown together in theembodiment illustrated to avoid undue repetition of the description.

The reels 7 and 8 are driven by respective electric motor/ generators 20and 21, the construction of the motor/ generators being such that theycan be used alternatively as motors or as drag generators. In thisembodiment the reel 7 is the unwind reel and therefore themotor/generator 20 is operating as a drag generator, the

condition of operation being reversed when the direction of travel ofthe strip 6 is reversed.

Each pair of work roll chocks 9 and it) is provided with four electrictransducers 22 arranged in pairs 22a, 22b, 22c and 22d (reading fromleft to right in FIGURE 2). Each transducer produces an electric signalrepresentative of the respective distance between the work-roll chocks 9and 10 as measured by the transducer. These electric signals willtherefore also be representative of the distance, as measured by therespective transducer, between the axes of rotation of the work rolls 2and 3 as measured at the roll necks, these measurements includingappreciable errors owing to a reduction in the effective diameters ofthe work rolls under the influence of the pressure on the rolls by thestrip 6.

The operation of the control system is as follows:

The mill operator sets an output thickness gauge, represented herein bya dial on a circuit block 23, to indicate the thickness required for thereduced strip, and at the same time set a tension signal setting gauge,represented herein by a dial on a circuit block 24-, to give the properrange of tension as dictated by the operators experience for thematerial to be rolled, so that the strip will be coiled neatly andtightly on the reel 8 without danger of breaking. The mill is then putin motion.

The two transducers 22a are connected so that the signals they produceare combined to give an average signal and this combined signal is fedtogether with the combined signal from the two transducers 22b to anaveraging circuit 25. Similarly, the combined signals from thetransducers 22c and 22d are fed together to an averaging circuit 26 inwhich'they are combined. The outputs from the circuits and 26 aresupplied to a further averaging circuit 27, the output of which in turnis fed to the circuit 23. Thus, the signal received by the circuit 23from the transducers is the average of all eight transducers and is anaccurate representation of the distance between the axes of rotation ofthe work roll necks. The presence of the errors mentioned above preventsthis signal from being also an accurate representation of the height ofthe roll gap and the output thickness of the strip 6. The circuit 23produces a signal that is an accurate representation of the outputthickness in a manner described below, and this is compared with thereference set by the output thickness gauge. If the two signals do notcorrespond, showing that the output thickness does not correspond to thepreset thickness, then the circuit 23 produces a control signal which isused to actuate the tension control 24 and/ or the screw down motors 16in order to bring the output thickness to the desired value.

A suitable and well known averaging circuit for this application can bean operational amplifier employing negative capacitive feedback andoperative as an electrical integrating element or even a conventionalmotor driven potentiometer or the like. The circuit 23 can be a signalsumming amplifier such as shown on page 14 of the book Electronic AnalogComputers by G. A. Korn and T. Korn, McGraw-Hill Book Company (1952).

An additional gauge monitor 23 is provided on each side of the mill inorder to check the correct operation of the control system, and also togive indication of any long term changes in the system due, for example,to temperature changes, or aging or malfunction of any of the systemcomponents. In the embodiment illustrated these gauge monitors compriseflying micrometers disposed one on each side of the mill, the signalsprovided by the monitors 28 being fed to the circuit 23. These monitorsignals are employed in checking that the system is functioningcorrectly, but do not directly control the mill operation because of thelong time delay involved in their production.

If the signal from the monitors 28 is compared with the signal from thecircuit 27 significant difierences are found between the two. As statedabove, this difference is due to the flattening of the work rolls underthe effect of the pressure applied to them by the material passingbetween the rolls, and this flattening varies appreciably with changesin the properties of the strip and changes in the setting of the mill.It is proposed, in accordance with this invention, to compensate forthese errors by providing a signal which is a suitable measure of theamount of flattening encountered. This signal can be provided by twomethods which are alternatives of each other. In the first method theforce is measured directly by means of the strain gauges 17. In thesecond method the force is measured indirectly by determining thedifference between the preset roll spacing (which may be negative, i.e.the rolls are being forced together) as indicated by the positiongenerators 19, and the roll spacing as measured by the transducers 22.

The output thickness G of the material 6 can be represented by theequation G F s 1 where F is the force as measured by the strain gauges,M is the elastic coeificient of the mill and S0 is the preset spacing ofthe rolls, as indicated by the position generators 10. The outputthickness G can also be represented by the equation where W is theelastic coefficient of the work rolls 2 and 3 and Sw is the actualspacing as measured by the transducers 22, the component F W being thecorrection required to take account of the above described rollflattening.

The operation of the control apparatus of Canadian patent specificationNo. 571,793 is in accordance with Equation 1 above and, despite theundoubted advantages of such apparatus, as compared with the apparatusknown prior to the invention which is the subject of British patentspecification No. 571,793, the operation of the apparatus with therequired degree of accuracy requires the measurement of and compensationfor parameters which are not shown in the equation. The operation of theapparatus in accordance with this invention is in accordance withEquation 2 above and it can be shown that the parameters affecting themeasurements of Equation 1 are with the Equation 2 of the second order,so that the required order of accuracy can be obtained without the needto measure them. The equations also show that the force F of Equation 2can be replaced by suitable substitution of M and So of Equation 1.

In one particular form of the invention therefore the strain gauges 17are provided and produce a second signal which is combined in therequired proportions with the signal from the circuit 27, the resultantsignal being compared with reference signal and a control signal beingproduced which is supplied by the circuit 23 to control the striptension and the screw motors 16, as described above. In the otherparticular form of the invention the position generators 19 are providedand the signal they produce is compared with the average signal suppliedby the circuit 27, a proportion of the resultant signal being used tomodify the signal from the circuit 27. The modified signal is thencompared with the refference and a control signal produced which againis used in controlling the strip tension and/or the screw motors 16. 1

Referring now to FIGURE 4, a particular preferred form of the transducer22 will now be described. The major portion of the transducer isaccommodated in a bore 29 in the chock 9, so that it is housedcompletely within the body of the chock and is thereby protected againstthe deleterious effects of oil, dirt and mechanical shock and damage.The transducer proper consists of a differential transformer 30 which ismounted in a housing 31 with its operating plunger 32 protruding andengaging a slide 33. The plunger 32 is biased for movement (in adownward direction as seen in FIGURE 4) by a spring (not shown) mountedin the body of the transducer, while the slide 33 is biased by a spring34 for downward movement relative to the housing 31, so, that aprojecting end 35 thereof engages a reference anvil 36 which is screwedto the upper surface of the lower work roll chock 10. Thus, the spring34 maintains the elements 35 and 36 in close contact with one another,while the internal spring of the transducer maintains the plunger 32 inclose contact with the slide 33. The housing 31 is supported by a tube37 to which it is screw-threaded, the tube 37 being in turnscrew-threaded to another housing 38 that is bolted to a mounting plate39 supporting conduit 40 and connecting plug 41. The mounting plate 39is removably fastened to the upper face of the upper roll chock 9 (seealso FIGURES 1 and 2) and all the tranducers are fastened to it, so thatthe removal of the plate 39 will also remove all the transducerstogether as a unitary structure, eg when the rolls and their chocks areto be replaced.

Although a particular form of transducer has been described, it will beapparent that any other form of electrical transducer producing avoltage which varies in dependence upon the distance apart of two of itselements can be used. In some embodiments the transducer may not producean electric signal, but instead may produce a mechanical displacementwhich is applied to control a member of the circuit 23, although asignal-producing transducer will usually be desired. Moreover, althoughin the embodiment described the transducers employed are accommodated inrespective ones of the work roll chocks, in other embodiments they maybe mounted on the sides or the ends of the chocks and protected bysuitable shields.

We claim as our invention:

1. A control system for a rolling mill, comprising a pair of work rollsbetween which passes the material to be rolled, the system comprisingmeans for making a measurement that is eifectively a direct measurementof the distance between the axes of rotation of the work rolls and forproducing a first electric signal representative thereof, means forproducing a second signal representative of the separating forceproduced between the rolls with the material passing between them, meansutilizing the said first and second signals in the production of a thirdsignal representative of the output thickness of material that haspassed between the rolls, and means utilizing the said third signal forcontrolling the operation of said work rolls of the mill.

2. A control system for a rolling mill, the mill comprising a pair ofwork rolls mounted by their necks for rotation about their axes ofrotation and between which rolls passes the material to be rolled, thesystem comprising means for making a measurement between the roll necksthat is effectively a direct measurement of the distance between theaxes of rotation of the work rolls and for producing a first electricsignal representative thereof, means for producing a second signalrepresentative of the separating force produced between the rolls withthe material passing between them, means utilizing the said first andsecond signals in the production of a third signal representative of theoutput thickness of material that has passed between the rolls, andmeans utilizing the said third signal for controlling the operation ofsaid work rolls of the mill.

3. A control system as claimed in claim 1, wherein the said means forproducing a second signal comprise means for measuring the separatingforce produced between the work rolls by the material passing betweenthem.

4. A control system as claimed in claim 1, wherein the said means forproducing a second signal include 6 strain gauges interposed between thework rolls and the mill frame.

5. A control system as claimed in claim 1, wherein the said means formaking a measurement comprise two pairs of transducers, each pair beingdisposed at a different one of the two ends of each roll, the twotransducers of each pair being disposed on opposite sides of a planepassing through the aXes of rotation of the work rolls.

6. A control system as claimed in claim 1, wherein the said meansutilizing the third signal compare the third signal with a reference toproduce an error signal and employ the error signal in controlling thetension of the material passing between the work rolls.

7. A control system as claimed in claim 1, wherein the said meansutilizing the third signal compare the third signal with a reference toproduce an error signal and employ the error signal incontrolling theseparation setting of the work rolls.

8. A control system as claimed in claim 1, wherein the said meansutilizing the third signal compares the third signal with a reference toproduce an error signal and employs the error signal in controlling thetension of the material passing between the work rolls and incontrolling the separation setting of the work rolls.

9. A control system as claimed in claim 1, wherein the said means formaking a measurement comprise two pairs of differential transformers,each pair being disposed at a different one of the two ends of eachroll, the two transducers of each pair being disposed on opposite sidesof a plane passing through the axes of rotation of the work rolls, thedifferential transformers being so electrically connected that the saidfirst signal is representative of the average of the measurements of allthe transformers.

10. A control system for a rolling mill, the mill comprising a pair ofwork rolls mounted by their necks in roll chocks for rotation abouttheir axes of rotation and between which rolls passes the material to berolled, the system comprising distance measuring means for measuring thedistances between the associated pairs of roll chocks, which distancesare effectively a direct measurement of the distance between the axes ofrotation of the work rolls and for producing a first electric signalrepresentative thereof, means for producing a second signalrepresentative of the separating force produced between the rolls withthe material passing between them, means utilizing the said first andsecond signals in the production of a third signal representative of theoutput thickness of material that has passed between the rolls, andmeans utilizing the said third signal for controlling the operation ofthe work rolls of the mill.

11. A control system as claimed in claim 10, wherein the said distancemeasuring means comprise transducers associated with each pair of workroll chocks and accommodated within one of the chocks of each pairthereof.

References Cited by the Examiner UNITED STATES PATENTS 3,022,688 2/62Simms -56.2 3,062,078 11/62 Hulls 80-56 3,100,410 8/63 Hulls et al.80-56 FOREIGN PATENTS 571,793 3/59 Canada.

1,266,019 5/61 France.

WILLIAM J. STEPHENSON, Primary Examiner. LEON PEAR, Examiner.

1. A CONTROL SYSTEM FOR A ROLLING MILL, COMPRISING A PAIR OF WORK ROLLSBETWEEN WHICH PASSES THE MATERIAL TO BE ROLLED, THE SYSTEM COMPRISINGMEANS FOR MAKING A MEASUREMENT THAT IS EFFECTIVELY A DIRECT MEASUREMENTOF THE DISTANCE BETWEEN THE AXES OF ROTATION OF THE WORK ROLLS AND FORPRODUCING A FIRST ELECTRIC SIGNAL REPRESENTATIVE THEREOF, MEANS FORPRODUCING A SECOND SIGNAL REPRESENTATIVE OF THE SEPARATING FORCEPRODUCED BETWEEN THE ROLLS WITH THE MATERIAL PASSING BETWEEN THEM, MEANSUTILIZING THE SAID FIRST AND SECOND SIGNALS IN THE PRODUCTION OF A THIRDSIGNAL REPRESENTATIVE OF THE OUTPUT THICKNESS OF MATERIAL THAT HASPASSED BETWEEN THE ROLLS, AND MEANS UTILIZING THE SAID THIRD SIGNAL FORCONTROLLING THE OPERATION OF SAID WORK ROLLS O THE MILL.